Abstract: Disclosed is a method, system, vehicle, and computer program for improving heat release evaluation at a reciprocating combustion engine. The method comprises providing a model regarding volume deviations in the combustion chamber based on a first set of dynamic parameters of the combustion engine. Said model comprises volume deviations due to thermal changes, due to mass forces and due to pressure forces. The method comprises determining the first set of dynamic parameters relating to the combustion engine, and determining the volume deviation in the combustion chamber based on said provided model and based on said first set of determined dynamic parameters. The method comprises providing an adaption model for the combustion engine based on said determined volume deviation in the combustion chamber, and adapting the combustion engine control and/or a diagnostic system of the combustion engine based on said adaption model so that said heat release evaluation is improved.